B2B-2658: Implement GraphQL Resolver Cache for Customer query

- CR fixes (type hint and inline comments)

Author: rganin

app/code/Magento/GraphQlResolverCache/Model/Resolver/Result/ValueProcessorInterface.php

@@ -27,10 +27,10 @@ public function processCachedValueAfterLoad(ResolverInterface $resolver, string
     /**
      * Preprocess parent resolver resolved array for currently executed resolver.
      *
-     * @param array|null $value
+     * @param array $value
      * @return void
      */
-    public function preProcessParentValue(?array &$value): void;
+    public function preProcessParentValue(array &$value): void;
 
     /**
      * Preprocess value before saving to cache for the given resolver.